Exercise is a general term which may imply a multitude of outcomes. Aerobic exercise is designed to increase heart rate, circulation and improve overall cardiovascular fitness. Muscular exercise is designed to increase muscular tonicity by either eccentric or concentric contraction movements. Some exercises are designed to combine both aerobic and muscular workouts to produce a more uniform fitness.
In the past 100 years a variety of devices and machines have been developed that are muscle specific and efficient in exercising a single muscle or muscle group. A void, however, has existed in novel equipment that effectively strengthens and improves muscular function in the lower extremities. Specifically this void involves the quadriceps, hamstrings and gluteal musculature. Although many machines have duplicated each other to work and exercise the hamstrings, quadriceps and gluteals, there exists no better exercise than the squat to exercise all three muscle groups simultaneously. A squat or a squat exercise movement refers to the vertical bending at the knees to simultaneously elongate the quadriceps, hamstrings and calf muscles. The reverse movement which involves straightening of the femur tibial joint produces contraction of the hamstrings, quadriceps and gluteal muscles.
Unfortunately the squat exercise movement that is done frequently in juvenile and adolescent development is seldom performed by adults. Therefore, unless a person actively engages in sports activities from adolescence into adulthood, it may be difficult for one to perform repetitive squats with as little as one's own body weight. Squat machines routinely load the spine and lower extremities in either the vertical or horizontal position. In adults, this loading may prove difficult if not impossible due to compromise of spine, hip, knee and ankle stability. Degenerative changes in the disc, cartilage and/or ligaments can restrict this exercise movement in overweight persons simply because of pain.
Ideally a squat exercise movement is best performed by adults without vertical loading using only the body weight of the individual. This is accomplished by standing upright with the feet spread to shoulder width when squatting downward until the backs of the legs are parallel to the ground. Again, even this non-weight bearing squat movement frequently cannot be performed, because the individual's upper body weight exceeds the loading capacity of the lower extremity muscles and joints.